Greenacres Industries would be forced to shut down leaving 240 disabled workers unemployed if a case to go before the Fair Work Commission is upheld, Greenacres CEO Chris Christodoulou said on Monday.

The Health Services Union and United Voice will lodge an application in the Fair Work Commission today seeking to have all wage assessment tools removed from Australian Disability Enterprises (ADE), formerly known as sheltered workshops, and replaced with the Supported Wage System (SWS).

The SWS, created in the 90s, is used to assist disabled employees enter the open employment market. ADEs are government-subsidised businesses and usually support workers with greater needs and lower skills, some of whom are paid as little as $1 an hour.

The move by the unions, which is supported by the ACTU, comes after a landmark appeal in which a Federal Court judge found the Business Services Wage Assessment Tool (BSWAT), used by up to 60 ADEs, was discriminatory and its competency test was unfair and led to lower wages for disabled workers.

The legal victory could affect more than 10,000 workers.

David O'Byrne, acting national secretary of United Voice said the union had taken the action because it had an obligation to ensure that people were not unfairly discriminated against in their employment as a result of a disability.

"We're committed to working constructively with all employers to ensure that vulnerable workers are treated fairly and that we bring the tools used to assess the pay of people with a disability in line with the Federal Court judgment," Mr O'Byrne said.

The action was also in line with an Australian Human Rights Commission decision that the federal government take all necessary steps to transition to the SWS or an alternative tool approved by the Fair Work Commission, he said.

In a letter leaked to the Mercury, Mr Christodoulou has told employees, their parents and guardians that Greenacres would be seeking an Enterprise Agreement with its workers to circumvent any future decision by the Fair Work Commission over the widespread implementation of the SWS.

"We are not opposed to working with unions to negotiate a fair and reasonable assessment tool which is sustainable," Mr Christodoulou said. "But the SWS will almost certainly mean the closure of Greenacres because it artificially imposes wage increases for people with high support needs."

When contacted by the Mercury, Mr Christodoulou called for a commonsense approach.

"We are absolutely opposed to this matter being litigated and being determined by a court," he said.

Greenacres currently determines a worker's wage using its own competency assessment tool, which Mr Christodoulou explained was rights based in that it allowed workers to be evaluated every three months and gave them the option of having a union official present during the assessment.

Greenacres workers are paid on average $4.55 an hour, with the lowest paid workers on $2.30 an hour. Mr Christodoulou said that rate was higher than many other ADEs.

"If you calculate the level of our employees' supported wage with the pension that they receive, most of our workers would come close to earning the minimum wage," Mr Christodoulou said.

About 99 per cent of Greenacres workers were unable to find work in open employment and had to be constantly supported, trained, prompted and compensated for gaps in their work skills.

It is estimated that if Greenacres was forced to implement the SWS it would mean an increase in supported employees' wages of $1.7 million a year.

Greenacres is already operating at a $400,000-a-year loss.

"In the history of wage determination in Australia no other industry would be wiped out because of a decision of an industrial relations commission or court," Mr Christodoulou said.

Greenacres employees and their carers have been asked to attend a meeting to discuss the issue on May 21 at the City Diggers Club.